tango - it is possible to add it to the 4x version but this would require database/schema changes. Version 5.0 supports custom fields and is in beta testing right now.
Sanjay

the beta version was sent out to the people who originally signed up for beta testing. At this point there aren't any additional beta testers being added to the beta testing program.
With regards to a release date, I am hesitant to give a date because of past experience where people expect the date to be met no matter whatever effort is required. The module is still being tested and will be submitted to the release tracker once there is a confidence level that there isn't any major issues that are coming up.

Sanjay